Antenna system



May 13, 1952 N. UNDENBLAD 2,596,492

ANTENNA SYSTEM Original Filed Sept. 9, 1944 2. SHEETS-SHEET 1 INVENTOR M78 gzmdenblad A4 AM I :HQRNEY M 13, 1952 N. E. LINDENBLAD ANTENNA SYSTEM 2 SHEETS-SHEET 2 Original Filed Sefit. 9, 1944 QEGR E D/SPLHCEMEA/T Mysgzifiiblzd f latented May 13, 1952 ANTENNA SYSTEM Nils E. Lindenblad, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Original application September 9, 1944, Serial No.

553,321, now Patent No. 2,540,536, dated February 6, 1951.

Divided and this application October 19, 1949, Serial No. 122,260

12 Claims. I

The invention relates to radio detecting and ranging systems, commonly known as radar systems and particularly pertains to a novel antenna for such systems which utilize continuous wave transmission rather than pulse transmis- S1011.

The instant application is a division of copendlng U. S. application Serial No. 553,321 filed September 9, 1944 and entitled Obstacle Detection System, now Patent No. 2,540,536 issued Feb ruary 6, 1951.

In some radio detecting and ranging systems which are at present in common use, stored energy is discharged in spurts of short duration in order that high amplitude levels of radiated energy may be used. However, when pulses of short duration are used, wide band receivers are required. In this way, more noise is admitted which tends to oflset the gain in amplitude in the transmitted signal. In these systems, the primary object is the determination or recording of the time lapse between the transmission of a signal toward a reflecting object and its return. Accurate time measurements do not necessarily require the choice of wide band modulation methods, and it is an object, therefore, of the invention to utilize continuous wave systems for determining th distance and location of a reflecting object from a given location without requiring wide band modulation methods.

Another object of the invention is the provision of a radio directing and ranging system which depends upon the polarization sensitivity of a dipole for range indication. v

A further object of the invention is the provision of a new and improved antenna structure for use in a system as aforesaid.

Still another object of the invention is the provision of an improved means for rotating the plane of polarization of an ultra high frequency radiator.

Still a further object of the invention is the provision of means for rotating the plane of polarization of a high frequency radiator at a rate much greater than the physical speed of rotation of the rotating element.

The foregoing objects and other objects which may appear from the following detailed description are attained by providing a radio direction and ranging device utilizing a continuous wave transmitter and receiver connected to separate directive antennas which are locked together in the same direction so that their directivity patterns cover the same general area. The antennas justed in azimuth and elevation. The radiating means associated with each of the antennas is arranged to be rotated at a predetermined rate so that the plane of polarization of the transmitted signal is continuously rotated, while the plane of polarization of maximum sensitivity of the receiving antenna is simultaneously rotated at either the same rate or a different rate.

Arrangements are provided to vary the phase relationship between the planes of polarization of the transmitting and receiving antennas. The energy radiated from the transmitter is reflected from a distant reflective obstacle, and the reflected wave is picked up by the receiving antenna. Since the plane of polarization of the transmitted wave is constantly changing due to the rotation of the transmitting antenna, the plane of polarization of the received wave varies in accordance with the distance from a reflecting object to the transmitter and receiver. By suitably adjusting the phas of the plane of polarization of the receiving antenna with respect to that of the transmitting antenna, the received signal may be brought down to a minimum value.

It is then known that the receiving antenna is at right angles to the plane of polarization of the reflected signal. Thus by measuring the difference in the phase of the plane of polarization between the two antennas, a measure of the distance from the reflecting object to the trans mitter and receiver may be obtained.

Since the speed of rotation of a dipole may be limited by mechanical considerations, it is a further purpose of this invention to provide means affording an increased rate of rotation of the plane of polarization beyond that possible with direct mechanical rotation.

This may be accomplished by the use of a disc shaped radiator of such dimensions that it exhibits diametrical half-wave tuning; Energy to be radiated by such a disc may then be induced therein with the plane of polarization in any direction in the plane of the disc, the polarization depending purely on the geometry of the application of the feed. Now'if the means for coupling energy from a transmitter to the disc is arranged to have its degree of coupling varied around the circumference of the disc more rapidly than the disc rotates, an increased rate of rotation of the plane of polarization may be obtained. This may be accomplished by utilizing a number of separate coupling members arranged like gear teeth on the circumference of the disc and a difierent number of similar couare preferably arranged to be simultaneously adpling members surrounding the disc and connected to a source of high frequency energy such as a transmitter. The number of coupling members on the disc and the number surrounding the disc must bear a primed relationship, that is there must be no least common denominator other than unity, so that only one pair of coupling members can coincide at any given instant. The arrangement is somewhat similar to the calibration of a Vernier scale. A Vernier scale includes two slideable parallel scales of unequal numbers of divisions on the two scales. Thus one scale may have nine or eleven divisions in the space occupied by ten on the other scale. If it is assumed that a pair of divisions, one on each of the two scales, coincide, then by sliding one scale relative to the other by a distance of a half division, the places where the graduations coincide has moved to where there was before the greatest divergence. This distance is much larger than the actual motion of the scales. In the same way the point of coincidence between coupling members of the present antenna is moved around the entire circumference of the disc by a fraction of a revolution of the disc.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which Figure 1 illustrates an embodiment of the present invention, while Figures 2 and 3 are sectional, elevation, and plan views of a radiator utilizing the principles of an aspect of the present invention, while Figure 4 is a linear development of a portion of the structure shown in Figures 2 and 3 for the purpose of making the operation of the device more clear.

Referring now to Figure 1, there is shown a continuous wave transmitter in operating at a frequency, for example, of 300 megacycles corresponding to 1 meter wavelength. The output from the transmitter is applied to a directive antenna including a novel rotatable dipole radiator ll, later to be described in greater detail, and a parabolic reflector I2 so arranged with respect to radiator l I as to obtain a high directive beam energy along the axis of reflector I2. Mounted closely adjacent to the transmitting antenna is a receiving antenna, including a rotatable dipole radiator 2i and a parabolic reflector 22 similar to the radiator and reflector of the transmitting equipment. The axes of directivity of antennas l2 and 22 should be arranged substantially parallel to one another at all times. This may be assured by providing an arrangement (not shown) whereby the antennas are locked together in a gimbal arrangement so that they may be simultaneously swung in any direction in azimuth or elevation. Transmitting dipole H is arranged to be rotated at any given rate of speed by motor M and receiving dipole 2| is similarly arranged to be rotated by motor M at a slightly difierent rate of speed due to the interposition of gear boxes 8| and 82 having difierent gear ratios. These motors may be synchronous motors driven from a conventional alternating current power line as indicated.

The energy from transmitter 19 radiated from rotating dipole l I is radiated in a sharp directive beam of energy substantially along the axis of reflector l2 and directed toward the object to be detected (not shown). A small portion of the energy striking the object is reflected back to the receiving antenna reflector 22 and applied to the receiving dipole 2|. Since the two antennas are always directed simultaneously in the same direction, the object to be detected is within the zone of maximum response of the receiving antenna. The energy picked up by the dipole 2| may then be applied to receiver 24 by means of transmission line TL.

Tone wheels and 85 are provided on the rotating shafts of each of the antennas in order to obtain alternating current waves of frequencies proportional to the speed of rotation of the plane of polarization of each of the antennas. The two alternating current waves thus generated, of frequencies f1 and f2, are applied to a mixer 87 and the difference frequency obtained by their heterodyne. The difference frequency is passed through a phase shifter 88 and from there connected to the sawtooth wave generator 99. The difference frequency thus controls the synchronization of generator 96. The output of generator 99 is applied to the horizontal deflection plates $2 of oscilloscope HQ. Thus the difference in actual rotating speeds of the plane of polarization of the transmitted signal and the received antenna controls the horizontal sweep of the oscilloscope in such a way that the position along the sweep is proportional to the angle of deviation between the two antennas. The signal picked up by the receiving antenna and rectified and amplified in receiver 24 is applied to the vertical deflection plates 9! of oscilloscope llfl. Thus the null in reception as the receiving antenna passes through a plane at 90 to the plane of the received signal is recorded as a dip in the distributed amplitude curve on the scale of the oscilloscope. The position of this dip in relation to a reference scale (not shown) on the screen of oscilloscope H0 is a measure of the distance between the equipment and the reflecting object to which the dip is due. Even though there may be a multiplicity of reflecting objects within the zone of maximum response of the antennas, it is thus possible to individually distinguish between these targets.

As intimated above, a preferred form of rotating antennas for the present invention is shown in Figures 2, 3 and 4. In Figure 2 there is shown in elevation and partly in section, an

antenna structure including a disc shaped radiafter it having a diametral dimension of the order of one-half of the operating wavelength. Energy to be radiated by such a disc may be induced therein with the subsequent plane of polarization oriented in any direction in its own plane withequal facility. The polarizationof the radiated energy is dependent only upon the geometry of the application ofthe feed. Thus if a feed point for the disc is rotated about the axis of the disc, the plane of polarization of the radiated energy is rotated. The radiating disc iil is energized by the coupling between the teeth ii on disc 353 and teeth id on the surrounding energizing structure.- It will be noted from an inspection of Figures 2 and 3 that there is a different number of teeth 4 than the number of teeth ii; Due to the different numbers of teeth, there is at any instant only one point on the circumference of disc t?) where a tooth M is in exact alignment with a tooth M of the surrounding energizing structure. This point is at the bottom of Figure 3 and at the center of Figure 4, wherein the tooth structure has been developed along a straight line. The point of greatest co'upling thus occurs at the bottom and the plane of polarization of the radiated energy is in the plane passing through that tooth and the center of disc 58. Thegcoupling gradually decreases along the length of the circumference of disc 40 to a minimum at the top of the figure in Figure 3 and at the extreme ends of the showing in Figure 4. This is shown graphically by curve 45, in Figure 4. Now, the disc 40 will be considered as operating in a counter-clockwise direction as shown by the arrow in Figure 3. This is shown by the'left-to-right arrow in Figure 4. A very small angular movement of disc 40 will bring the teeth to the left of the bottom in Figure 3 in alignment, while the coupling between the teeth at the bottom is decreased. Thus the plane of polarization of the received radiated wave is shifted by a considerable angle for only a very small angular rotation of disc 39. Rotating disc 4!! half the angular distance between successive teeth brings the point of greatest coupling to the top of Figure 3. The original point of greatest coupling now has the lowest coupling. Thus the plane of polarization is rotated 180 for only a very few degrees or rotation of disc 46.

The teeth 44 are constructed as part of a housing which either wholly or partially constitutes a centrally energized resonant cavity. The details of construction of the resonant cavity are shown in more detail in Figure 2 in sectional elevation. The cavity has an overall width of the order of one wavelength. It has turned over one-quarter wave portions at each end across which the energizing transmission lines TLi and TLz are connected. By shifting the point of connection of the center conductors of TL1 and TLz along the length of quarter-wave portions 46 and ii, an impedance matching of the transmission lines to the antenna cavity may be allowed. The transmission lines TL], and TLz are connected to gether to a single output transmission line TL with the proper relative lengths of transmission line 'ILi and 'ILz to assure the proper phase of energization of the two ends of the cavity. The principles of operation of this portion of my invention are the same as involved in the invention disclosed in my prior application, Serial No. 513,691, filed December 10, 1943, now U. S. Patent 2,423,150, issued July 1, 1947, to which reference may be made for a more complete description.

While several specific embodiments of the present invention have been illustrated, it should be clearly understood that it is not limited thereto since many modifications may be made in the several elements employed and in their arrangement without departing from the spirit and scope of the invention.

Iclaim:

1. A system for radiating an energy wave of rotating polarization including av substantially planar radiator capable of having energy induced therein with the subsequent plane of polarization oriented equally well in any direction in the plane of said radiator, means for rotating said radiator, means for couplingsaid radiator to a source of high frequency energy, and means for causing the direction in which said energy is induced in said radiator to progress around said radiator as said radiator is rotated.

2. A system for radiating an energy wave of rotating polarization including a substantially planar radiator capable of having energy induced therein with the subsequent plane of polarization oriented equally well in any direction in the plane of said radiator, means for rotating said radiator, and means for coupling said radiator to a source of high frequency energy, said means including coupling elements on said radiator and stationary coupling elements, the numbers of said elements being difierent. 1

3. A system for radiating or receiving an ellergy wave of rotating polarization including a substantially planar radiator capable of having energy induced therein with the subsequent plane of polarization oriented equally well in any direction in the plane of said radiator, means for rotating said radiator, and means for transferring high frequency energy to and from said radiator, said means including coupling elements on said radiator and stationary coupling elements, the numbers of said elements being different.

4. A system for radiating or receiving an energy wave of rotating polarization including a rotatably disc radiator, said radiator bearing a number of coupling members uniformly spaced about the axis of rotation of said disc, a number of stationary coupling members uniformly spaced about the axis of rotation of said disc, the number of said stationary members being difierent than the number of said members born by said disc, and means for coupling a high fre quency energy transducer to said stationary coupling members.

'5. A system for radiating or receiving an energy wave of rotating polarization including a rotatable disc radiator, said radiator bearing a number of coupling members uniformly spaced about the axis of rotation of said disc, a number of stationary coupling members incommensurate with the number of said first mentioned coupling members and uniformly spaced about the axis of rotation of said disc, and means for coupling a high frequency energy transducer to said stationary coupling members.

6. An antenna including a disc shaped radiator of such dimensions that it exhibits diametrical half-wave tuning, means for rotating said disc about its axis, said disc having a number of teeth around its periphery, a number of teeth differing from the number on said disc arranged around the circumference of said disc and in cooperative relationship with the teeth on said disc, and coupling means for high frequency energy connected to the second mentioned teeth.

7. An antenna including a disc shaped radiator of such dimensions that it exhibits diametrical half-wave tuning, means for rotating said disc about its axis, said disc having a number of teeth around its periphery, a number of teeth differing from the number on said disc arranged around the circumference of said disc and in cooperative relationship with the teeth on said disc, and coupling means for high frequency energy connected to the second mentioned teeth, one of the teeth on said disc always being in capacitive coupling arrangement with one of the teeth around said disc.

8. An antenna including a plane conductive sheet having channel members along at least a pair of opposing portions of the edges of said sheet, the depths of said channels being of the order of one-quarter of the operating wavelength, transmission lines coupled across said quarterwave channels, the distance between said channels being of the order of one-half of the operat ing wavelength, a disc shaped radiator having a transverse dimension of the order of one-half of the operating wavelength rotatably mounted over the open space between said channels, said disc carrying a number of teeth arranged around, and at a uniform distance from, the axis of rotation of said disc, a number of stationary teeth differing from the number carried by said disc uniformly spaced around the axis of rotation of said disc and in coupling relation with the teeth carried by said disc.

9. An antenna including a plane conductive sheet having channel members along at least a pair of opposing portions of the edges of said sheet, the depths of said channels being of the order of one-quarter of the operating wavelength, transmission lines coupled across said quarter-wave channels, the distance between said channels being of the order of one-half of the operating wavelength, a disc shaped radiator having a transverse dimension of the order of one-half of the operating wavelength rotatably mounted over the open space between said channels, said disc carrying a number of teeth arranged around, and at a uniform distance from, the axis of rotation of said disc, a number of stationary teeth differing from the number carried by said disc uniformly spaced around the axis of rotation of said disc and in coupling relation with the teeth carried by said. disc, said stationary teeth being conductively connected to the free edges of said quarter-wave channels.

10. An antenna including a plane conductive sheet having channel members along at least a pair of opposing edges of said sheet, the depths of said channels being of the order of one-quarter of the operating wavelength, transmission lines coupled across said quarter-wave channels, the distance between said channels being of the order of one-half of the operating wavelength, 9. disc shaped radiator having a transverse dimension of the order of one-half of the operating wavelength rotatably mounted over the open space between said channels, said disc carrying a number of teeth arranged around, and at a uniform distance from, the axis of rotation of said disc, 9. number of stationary teeth differing from the number carried by said disc uniformly spaced around the axis of rotation of said disc and in coupling relation with the teeth carried by said disc, said stationary teeth being connected to said plane conductive sheet.

11. An antenna system for transferring wave energy of rotating polarization between free space and a utilization device, including a plane conductive surface member having a serrated aperture therein, a conductive serrated disc arranged in said aperture for rotation therein with respect to said conductive surface member, the number of serrations in said disc diifering from the number of serrations in said conductive surface member, wall members behind said conductive surface member forming a resonant cavity therewith, and means to couple said utilization device to said resonant cavity.

12. The antenna system for transferring wave energy of rotating polarization between free space and a utilization device, including a plane conductive surface member having a serrated aperture therein, a conductive serrated disc arranged in said aperture for rotation therein with respect to said conductive surface member, the number of serrations in said disc differing from the number of serrations in said conductive surface member bearing a prime relationship to each other, wall members behind said conductive surface member forming a resonant cavity therewith, and means to couple said utilization device to said resonant cavity.

REFERENCES CITED FOREIGN PATENTS Country Date Great Britain Jan. 26, 1949 Number 

